title: RIT2, a neuron-specific small guanosine triphosphatase, is expressed in retinal neuronal cells and its promoter is modulated by the POU4 transcription factors.
abstract: OBJECTIVE
  Ras-like without CAAX 2 (RIT2), a member of the Ras superfamily of small guanosine triphosphatases, is involved in regulating neuronal function. RIT2 is a unique member of the Ras family in that RIT2 is preferentially expressed in various neurons, including retinal neurons. The mechanisms that regulate RIT2 expression in neurons were studied.
  
  
  METHODS
  Reverse transcription-quantitative PCR (RT-qPCR), immunohistochemistry, western blotting, bioinformatic prediction, electrophoretic mobility shift assay (EMSA), and cell transfection methods were used.
  
  
  RESULTS
  With immunohistochemistry of the mouse retina, RIT2 protein was detected in the ganglion cell layer (GCL), inner plexiform layer, inner nuclear layer, and outer plexiform layer, with the strongest staining in the GCL and the inner plexiform layer. RT-qPCR combined with laser capture microdissection detected Rit2 messenger RNA in the GCL and the inner nuclear layer. Western blot analysis showed a large increase in the RIT2 protein in the retina during maturation from newborn to adult. Transient transfection identified the 1.3 kb upstream region of human RIT2 as capable of driving expression in neuronal cell lines. Based on the known expression pattern and biological activity, we hypothesized that POU4 family factors might modulate RIT2 expression in retinal ganglion cells (RGCs). Bioinformatic analyses predicted six POU4 factor-binding sites within the 1.3 kb human RIT2 promoter region. EMSA analyses showed binding of POU4 proteins to three of the six predicted sites. Cotransfection with expression vectors demonstrated that POU4 proteins can indeed modulate the human RIT2 promoter, and that ISL1, a LIM homeodomain factor, can further modulate the activity of the POU4 factors.
  
  
  CONCLUSIONS
  These studies confirm the expression of RIT2 in retinal neuronal cells, including RGCs, begin to reveal the mechanisms responsible for neuronal expression of RIT2, and suggest a role for the POU4 family factors in modulating RIT2 expression in RGCs.
authors.affiliation: The Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
authors.forename: Ling
authors.initials: L
authors.lastname: Zhang
authors.forename: Karl
authors.initials: K
authors.lastname: Wahlin
authors.forename: Yuanyuan
authors.initials: Y
authors.lastname: Li
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Masuda
authors.forename: Zhiyong
authors.initials: Z
authors.lastname: Yang
authors.forename: Donald J
authors.initials: DJ
authors.lastname: Zack
authors.forename: Noriko
authors.initials: N
authors.lastname: Esumi
mesh_terms: D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D045744:Cell Line, Tumor; D019295:Computational Biology; D005786:Gene Expression Regulation; D006023:Glycoproteins / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009928:Organ Specificity; D050809:POU Domain Factors / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011485:Protein Binding; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D055351:Retinal Neurons / Q000201:enzymology*
chemical_list: D006023:Glycoproteins; D009419:Nerve Tissue Proteins; D050809:POU Domain Factors; D012333:RNA, Messenger; C089283:Rit2 protein, mouse; D020559:Monomeric GTP-Binding Proteins; C583559:RiT2 protein, human